- Low ecological validity = experiment was conducted in a controlled observation - infant may be unfamiliar with surroundings so more likely distressed
- categories not always applicable (nomothetic) (main and cassidy 1998) suggested that infants do not all fit into the 3 categories introduced by ainsworth or may not at all. They found another type of attachment (disorganised)
- culturally biased = SS was conducted in the USA. criteria used to criticise infants are based on US values e.g Japanese children were seen more as insecure resistant (spent most of their time with mother) whereas german infants were insecure avoidant (germans value independence)
- observation was a snapshot of behaviour, not taking into consideration of other factors like child's relationship with other family members or behaviour in familiar environments